Enterococcus faecalis requires unsaturated fatty acids to overcome toxicity of environmental saturated fatty acids.

Enterococcus faecalis synthesizes phospholipids from either de novo synthesized or exogenous fatty acids. However, environmental saturated fatty acids are toxic to E. faecalis. The mechanism of toxicity is unknown. We report that saturated acids block growth by efficiently repressing transcription of the fatty acid biosynthesis (fab) genes, resulting in blockage of the synthesis of unsaturated fatty acyl chains. Saturated fatty acid toxicity depends on the chain length of the acyl chains. Growth was restored in the presence of toxic saturated fatty acids by the increased de novo unsaturated fatty acid synthesis, resulting from the deletion of the fabT gene, the repressor that regulates (fab) gene transcription. The addition of unsaturated fatty acids to the medium also restored growth in the presence of toxic saturated fatty acids. Overexpression of AcpA, the fatty acid synthesis acyl carrier protein, also gave increased de novo synthesis of unsaturated fatty acids and restored growth.